In a cordless extension phone system, in an event where a base unit or an extension unit is operated, display devices provided in the base unit and the extension unit are allowed to display a phone number and other party's information, and the cordless extension phone system is used so as to make a convenience of a dial operation and a call operation and to ensure the same. Moreover, in an event of receiving an incoming call, the cordless extension phone system is used so as to issue a notice on such incoming, and to display the other party's information.
Moreover, a system is known in public, which stores, in a base unit and a plurality of extension units, phone book data recording therein phone numbers and other party's information, both being used in the base unit and the extension units, and in an event where the base unit or the extension unit is operated, reads out the phone book data and displays the phone number and other party's information on a display device of the base unit or the extension unit (for example, refer to Patent Documents 1 and 2).